1. Field of the Invention
One or more embodiments of the present invention relate to audio coding, and more particularly, to a surround audio coding method, medium, and system for encoding and/or decoding an audio signal.
2. Description of the Related Art
Generally, multi-channel audio coding includes waveform multi-channel audio coding and parametric multi-channel audio coding. The waveform multi-channel audio coding typically further includes moving picture experts group (MPEG)-2 MC audio coding, AAC audio coding, and BSAC/AVS MC audio coding, for example. In the waveform multi-channel audio coding, 5 channel signals may be encoded by an encoder terminal and 5 encoded channel signals may be received and ultimately decoded by a decoding terminal. The parametric multi-channel audio coding typically includes MPEG surround coding, where a multi-channel signal may be encoded and 1 or 2 encoded channel signals may be received and ultimately decoded to output 6 or 8 multi-channels, for example.
Here, such MPEG surround coding uses a first 5-1-5 tree structure, illustrated in FIG. 1A, or a second 5-1-5 tree structure, illustrated in FIG. 1B, in order to decode such a signal to multi-channels up-mix. The tree structures receive a down-mixed mono signal, i.e., a signal that has been encoded from multi-channel signals and output as a mono signal, and up-mixes the mono signal to multi-channel signals of a Front Left (FL) channel, a Front Right (FR) channel, a Center (C) channel, a Low Frequency Enhancement (LFE) channel, a Back Left (BL) channel, and a Back Right (BR) channel, using combinations of 1-to-2 (OTT) modules. Here, the up-mixing of the mono signal through the stages of OTT modules can be accomplished with previously generated spatial information of Channel Level Differences (CLDs) and/or Inter-Channel Correlations (ICCs), with the CLD being information about an energy ratio or difference between predetermined channels in multi-channels, and with the ICC being information about correlation or coherence corresponding to a time/frequency tile of input signals. With respective CLDs and ICCs, each staged OTT can up-mix a single input signal to respective output signals through each staged OTT.
Referring to FIG. 1A, in the first 5-1-5 tree structure, the first module OTT0 outputs a signal including mixed information for FL, FR, C and LFE channels, and a signal including mixed information for BL and BR channels.
Similarly, referring to FIG. 1B, in the second 5-1-5 tree structure, the first module OTT0 outputs a signal including mixed information for FL, BL, RF and BR channels, and a signal including mixed information for C and LFE channels. However, when selective decoding (“pruning”), e.g., if only selective channels are desired, the inventors have found it difficult to selective decode the different channels in either of the first or second 5-1-5 tree structures without performing all stages of OTT module decoding. For example, though an output of the OTT0 modules of either first or second 5-1-5 tree structure could potentially be sampled, they are up-mixed signals representing information for a number of front channels and back channels mixed together and would not be properly representative of any one selective channel, such as if a stereo signal of left and right channels was desired.
Accordingly, embodiments of the present invention overcome the above drawbacks.